So I asked about minima safety separation between landing and crossing RWY a/cs.
Well, that's just the pure art of aerodrome control! ;D
Unless you have strict values published in your Manual, you're on your own judgement here. So it is all safe if you decide it is... until it's too short! Use the licence :)
What different from lining-up a/c preparing for take-off and crossing RWY?
A taxiing aircraft is not going airborne, so if you screw it up - just send approaching traffic for go-around and you're fine. But if we are speaking about departure/arrival separation - you have to consider the separation between departing a/c and a/c possibly executing a missapp. So the difference is huge.